Plus, the actor reveals the inspiration behind his performance this fall.

In a tweet, creator Dan Fogelman wrote, "Season 3. Brace yourselves. #ThisIsUs," alongside a photo with what appears to be a younger version of William because he's not sporting the distinguished gray hair fans were introduced to in Season 1. Cephas Jones, who is nominated for an Emmy as Outstanding Guest Actor in a Drama Series, has recurred on the show, despite William's death in the Season 1 episode, "Memphis."

The sight is enough to make any fan well up. But, wait, who's the baby? Read on to see our theories on this perplexing and exciting Season 3 teaser.

Is it a flashback?

Clearly William is younger, but it's not the young version of William that fans have seen, played by Jermel Nakia. So if this image is from a flashback, it would be set in a time that fans haven't seen in William's life — somewhere between the '70s and now. Perhaps Rebecca babysat Randall's daughters and invited William to see them?

Viewers will learn more about the character of Nicky during this season's Vietnam storyline.

Does Randall have biological siblings?

The baby that William is holding could just be a friend's kid, but it could very well be his own. Despite meeting some of his family down in Memphis, Randall didn't have very long with William before he passed away. Surely there have to be some secrets that remain between the father and son, and another child could very well be the answer. Of course, it's a little presumptuous and early to tell, but it's not out of the This Is Us realm of possibility.

Could it just be a dream?

In a dream world, a lot of things would have been different for the characters of This Is Us. From older Jack's appearance in the Season 2 finale to Randall's hallucination sequence with Jack at the family cabin in Season 1, there are plenty of possibilities.

Regardless of these theories, one thing is for certain: William will return in Season 3. Hooray!